Radio Frequency Identification (RFID) uses electromagnetic fields to identify and track tags attached to objects. The RFID tags contain identity information. In response to the interrogating signals from the RFID readers, the RFID tags may communicate a response signal and allow identification by the reader. RFID technology is now used in a lot of commercial and industrial activities. For example, an RFID tag attached to a car during production can be used to track its progress through the assembly line; attaching RFID tags to livestock allows for identification of animals; and an RFID tag attached to pharmaceuticals can be used to track the pharmaceuticals through warehouses.
ISO/IEC 14443 is an international standard that defines proximity cards used for identification, and the transmission protocols for communicating with it. Collision resolution is an integral part of the ISO/IEC 14443A collision aware protocol. During Request Type A (REQA) and Answer to Request Type A (ATQA) initialization sequences, misinterpretation of the decoded bits may occur because the ATQA response is short without cycle redundancy check. Other reasons for misinterpretation include insufficient signal to noise ratio (SNR), an initial collision of a plurality of RFID tags, or a mixture of both. Full anti-collision protocols can be used to prevent the collisions. In addition, the collisions when they occur can be detected and classified to provide more precise interpretation of the decoded response signals.